Spark plug



Sept. 15,- 1942. w. F. HELLER SPARK PLUG Filed Jan. 18, 1941 9Min@afg/??? Gtiorncgs s l l 9.

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- Patentedsept. 15,194.21

SPARK PLUG Walter F. Heller, Flint, Mich., assigner to General MotorsCorporation, Detroit, Mich., a corporation of Delaware ApplicationJanuary 18, 1941, Serial No. 375,002

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This invention has to do with improvements in spark plugs having astheir object lengthening of the life of the electrodes and consequentlythe useful life of the plug.

Spark plug electrodes are subject to wear and deterioration due toerosion and corrosion. Erosion is produced by the action oi' the sparkin mechanically wearing away the metal of the electrode as well asburning the electrode metal and sputtering it as the result of highpotential and heat differential. It has been found that the rate oferosion increases with the temperature.

Corrosion of the electrodes is produced by the combustion gases Hz andcarbon monoxide and the oxidizing gases, oxygen, steam and carbondioxide. The principal corrosive acids present in the combustion chamberare sulphur compounds and lead compounds'. As in the case of erosion,corrosion increases directly as the temperature. It is the object of thepresent invention to provide a spark plug'electrode construction bywhich the electrode will be maintained at lower temperature and hencecorrosion and erosion will be reduced and the life of the plug will belengthened.

In the drawing:

Figure 1 is a vertical section through a spark plug embodying myinvention.

kThe most desirable material for the goodheat conducting filler iscopper although other materials having good heat conductivity, such assilver, may be used. .Y

In case of most severe service it may be desirable to employ tips ofmaterial more resistant to corrosion than the material used for thetubular electrode, such as platinum or platinum alloys includingplatinum-rhodium, platinumiridium, and platinum-rubidium alloys.

Referring now to the form shown in Figure 1, I0 indicates the insulatorwhich may be either of the sintered oxide ror porcelain type. Theinsulator is mounted in the usual shell indicated at I2. Both the centerand side electrodes comprise a vtubular shell Il made of the describedheat and corrosion resistant materials filled with good heat conductingmaterial indicated at I6, preferably'copper. To the ends of theelectrodes are secured tips i8 of material resistant to spark erosion aswell as corrosion. This latter material may be the same' as the materialof the tubular portion or may consist of platinum or platinum alloys aspreviously mentioned.

The upper end of the central electrode is indicated as in contact withthe enlarged upper portion 20 having a projecting terminal forengagement with the spark plug lead. The portion 20 Figure2 is a similarview showing a modified 30 may be welded or otherwise secured to thelower form of the invention.

Figure 3 is a fragmentary view showing a slight modification of theinvention shown in Figure 1.

Figures 4, 5 and 6 are similar views showing modifications.

Figure '1 is the vertical section through another form of my invention,the spark plug being illustrated as provided with a radio shield.

In all ofthe forms of the invention illustrated the center electrodesand, if desired, the side electrodes as well, are in the form of hollowtubes of material resistant to heat and corrosion filled with materialof very good heat conductivity. The tubular electrodes are preferablyclosed at the sparking ends by tips made of material reslstant toerosion caused by sparking as well as to corrosion.

I have found that the tubular electrode as well as the tip may be madeof nickel, nickel alloys, tungsten, stainless steels or similarmaterials. An especially desirable alloy is one consisting ofapproximately 2% manganese, 31/2% chromium, .02% barium and the balancenickel; this alloy being described and claimed in Ranportion of theelectrode but is preferably simply in contact with it.

The electrode assembly is secured in the insulator I0 preferably bymeans of a conducting seal 22 of the type described and claimed inSchwartzwalder and Kirk Patent 2,106,578, granted January 25, 1938, asimproved in accordance with the invention described and claimed inSchwartzwalder and Rulka application Serial No. 343,808, filed July 3,1940. The seal 22 consists essentially of a mixture of glass andpowdered metal, for example, copper, iron, cobalt, nickel, tungsten ormolybdenum. Of these copper is to be preferred. As described in saidapplications the parts are assembled with the sealing material in place.In the form illustrated in Figure 1 the sealing material is introducedin the form of an annular pellet. 'I'hereafter the assembly is heated tofuse the glass and while the glass is still soft the electrode isadvanced to the position shown in Figure 1. The sealing material oncooling forms an excellent gas-tight bond between the electrode and theinsulator. The

dolph Patent No.1,9'76,295, issued October 9, 1934. 53 metal included inthe sealing material assists in conducting the heat away from the centerelectrode.

The tubular electrode as shown in Figure l may be made in various ways.Thus a copper filled rod or bar may be swedged or rolled down to thedesired diameter and cut to length and the tip may then be welded to oneend. I have found it p culariy advantageous when welding the tip to metubular electrode to use the so called percussion method of Weldingwhich consists essentially in employing a welding circuit includingcondenser` which is arranged to discharge while the tip and the head ofthe electrode e. "e close together and after the discharge the parts areengaged thereby forming a good weld Without the application of suhicientheat to cause the copper :filling to flash through the joint therebyexposing it to corrosion.

in the inodication shown in Figure 2 the side electrode is U -shape andis provided with a tip le welded to the side thereof. The upper end ofthe lower of the central electrode is provided ith a flange 24 restingon a shoulder provided in the bore ci the insulator lil'. The lower endthe upper part of the center electrode Contact with the goed heat conor?the lower part of the center The electrode assembly is secured in 'ef-nsoi the heat conducting seal 2t :Si ....L' s

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rm of a disc 34 suitably seoni o1' the shell and having ons 36 whichcooperate with de. Similar side electrodes are and 5. In all these formsoi .filling ci goed heat conduct- "ed from the side electrodes. someinstances because 1"ode is provided with a good ath th'iough the plug e"For cooling.

lin the modication shown in Figure E the lower end of the centralelectrode is provided with an enlarged tip 40 welded to the copper nlledtubular shank as described in connection with Figure l.

There is illustrated in Figure 7 a further modiiication which has provento be especially good after extensive tests in airplane engines. Here 42indicates the shell in which is secured insulator 4I preferably composedchieily of sintered oxides such as aluminum oxide. To the lower end ofthe shell is welded the electrode I6 which may be made of stainlesssteel, nickel or nickel alloys. The center electrode comprises a lowerportion I8 made of erosion and corrosion-resistant material, preferablythe nickel-manganese-barium-chromium alloy disclosed in the saidRandolph patent. This electrode section is drilled out and illled withcopper or other good heat conducting material. The copper may be cast inor fused in place or, ii desired, the copper insert in the form of awire may be secured in place by silver solder using any suitable flux inthe customary manner. It will be noted that the interior of the bore 50of the insulator is Drovided with a wavy thread as shown or otherirregular contour and with a shoulder 52 on which seats iiange 54 formedat the upper end of electrode section 48. 56 indicates the upperelectrode section and 5B the conducting glass seal. lThe parts areassembled in the manner previously described; that is the conductingglass seal preferably consisting of a mixture of copper and Pyrex glassas described in the said Schwartrwalder and Rulka application is made inthe form of pellets and placed in the bore after the lower electrodesection has been positioned as shown. Thereafter the insulator is heatedto melt the glass and the upper electrode section 56 is then forced intothe desired position causn ing the molten sealing material to surroundand grip the threads on the upper electrode section and at the same timeengage the threads provided in the bore in the insulator, thus lockingthe electrode assembly against displacement.

Insulator 44 is provided with an extension 5B of considerable lengthprotruding' beyond the upper electrode section 56. The upper electrodesection 56 is provided with. an ex ion 6D adf U ed tc be connected inany suitable manner wi the mari: ping lead.

this view the plug is illustrated as provided v; iii?. radio shieldingconsisting oi metal sleeve 52 having threaded engagement with shell 42and iined with insulating material 64. A C-shaped insulator 6G isengaged between the bottom of shield 62 and the top ot the shoulder onthe insuiator to hold it in position in the shell. The usual coppergasket is provided at 68 to receive the lower part of the shoulder ofthe insulator.

Spark plugs of the construction shown in Figure '7 have beensuccessfully tested in modern high speed aircraft engines and haveperformed exceptionally well. The electrodes have had unusually longlife and this improvement is to be a "ributed largely to the goodconducting path it Tlvll be understood that the construction sho Jpossesses high heat conduc i aim:

l. A spark plug comprising an insulator having a passage therein, anelectrode in said passage comprising a tubular sheath having its exposedend closed, said sheath being made oi corrosion-resistant metal and lledwith metal of high heat conductivity, and means for securing and sealingthe electrode in the insulator, said sealing means enveloping the openend of the sheath and the exposed portion of the metal oi high heatconductivity so as to protect it from contact with corrosive gases andconduct heat away from the electrode.

2. A spark plug comprising an insulator having a passage therein, anelectrode in said passage comprising a tubular sheath having its exposedend closed, said sheath being made of corrosionresistant metal and lledwith metal of high heat conductivity, a conducting seal comprisingceramic material bonded to the interior of the passage and securing theelectrode therein, said seal enveloping the open end of the sheath andthe exposed portion of the metal of high conductivity so as to protectthe latter from contact with corrosive gases and conduct heat away fromthe electrode.

3. A spark plug comprising an insulator having a passage therein, anelctrode in said passage comprising a tubular sheath having its exposedend closed, said sheath being made of corrosionresistant metal and lledwith metal of high heat conductivity, and a conducting seal comprising amixture of ceramic material and good heat conducting material, theceramic material being bonded to the interior of the passage andsecuring the electrode therein, said seal enveloping the open end of thesheath and the exposed portion of the metal of high conductivity so asto protect the latter from contact with corrosive gases and conduct heataway from the electrode.

4. A spark plug comprising an insulator and an electrode in theinsulator comprising a sheath of corrosion-resistant metal filled withmetal of high heat conductivity secured and sealed in the passage bysealing material of high heat conductivity, said sheath having itsexposed electrode end closed to prevent the corrosive combustion gasesfrom attacking the metal of high heat conductivity.

5. A spark plug comprising an insulator having a passage therethroughand an electrode mounted in the passage comprising an upper section anda lower section, the latter comprising a tubular sheath having itsexposed end closed, said sheath being made of corrosion-resistant metaland lled with metal of high heat conductivity, and a seal having goodheat conductivity fused therein connecting said sections and securingthem in place.

6. A spark plug comprising an insulator having a passage therethroughand an electrode mounted in the passage comprising an upper section anda lower section, the latter comprising a tubular sheath having itsexposed end closed, said sheath being made of corrosion-resistant metaland filled with metal of high heat conductivity, a seal having goodheat, conductivity fused therein connecting said sections and securingthem in place and said seal comprising a mixture of glass and metal. y

'1. A spark plug comprising an insulator having a passage therein, anelectrode in said passage comprising a tubular sheath having its exposedend closed, said sheath being made of corrosionresistant metal andfilled with metal of high 'heat conductivity, and means for securing andsealing the electrode in the insulator, said sealing means being in goodvthermal contact with the open end of the sheath and the exposed portionof the metal .of high heat conductivity so as to protect it from contactwith corrosive gases and conduct heat away from the electrode.

8. A spark plug comprising an insulator having a bore therethrough, anelectrode in said bore comprising a tubular sheath having its exposedelectrode end closed, said sheath being made of corrosion-resistantmetal and lled with material of high heat conductivity, and means forsecuring and sealing the electrode in the insular bore, said sealingmeans surounding the said sheath and being in intimate contact therewithand with the wall of the bore so as to prevent passage of corrosivegases therethrough.

9. A spark plug comprising an insulator having a bore therethrough, anelectrode in said bore comprising a tubular sheath having its exposedelectrode end closed, said sheath being made of corrosion-resistantmetal and filled with material trode.

WALTER F. HELLER.

